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PubMed1991

Orientation bias of cat dorsal lateral geniculate cells: directional analysis of the major axis of the receptive field centre.

The receptive field centre of cells in the dorsal lateral geniculate nucleus were mapped as iso-sensitivity contours. 94% of the cells were found to have elliptical centres, and analysis of the major axis orientation showed that 29% and 59% of units had their major axis oriented within +/- 20 degrees of the radial and horizontal directions, respectively. The data for Y-cells showed a greater dispersion in their orientation biases (R = 0.57) compared with X-cells (R = 0.79). Nevertheless, a horizontal orientation bias was found in both classes of cells: 47% of Y-cells and 73% of X-cells. In addition, an examination of the major axis orientations was undertaken for cells with receptive field centres located along the radial direction of 35 degrees below the horizontal meridian. In this 35 degree Radial Group a horizontal bias was also confirmed. Analysis of the dispersion of major axis orientations with eccentricity from the area centralis showed a statistically significant decrease in scatter and, hence, indicated an increase in the horizontal bias with eccentricity.

Animals↗
PubMed1995

Express saccades in cat: effects of task and target modality.

Saccadic eye movements to visual, auditory, and bimodal targets were measured in four adult cats. Bimodal targets were visual and auditory stimuli presented simultaneously at the same location. Three behavioral tasks were used: a fixation task and two saccadic tracking tasks (gap and overlap task). In the fixation task, a sensory stimulus was presented at a randomly selected location, and the saccade to fixate that stimulus was measured. In the gap and overlap tasks, a second target (hereafter called the saccade target) was presented after the cat had fixated the first target. In the gap task, the fixation target was switched off before the saccade target was turned on; in the overlap task, the saccade target was presented before the fixation target was switched off. All tasks required the cats to redirect their gaze toward the target (within a specified degree of accuracy) within 500 ms of target onset, and in all tasks target positions were varied randomly over five possible locations along the horizontal meridian within the cat's oculomotor range. In the gap task, a significantly greater proportion of saccadic reaction times (SRTs) were less than 125 ms, and mean SRTs were significantly shorter than in the fixation task. With visual targets, saccade latencies were significantly shorter in the gap task than in the overlap task, while, with bimodal targets, saccade latencies were similar in the gap and overlap tasks. On the fixation task, SRTs to auditory targets were longer than those to either visual or bimodal targets, but on the gap task, SRTs to auditory targets were shorter than those to visual or bimodal targets. Thus, SRTs reflected an interaction between target modality and task. Because target locations were unpredictable, these results demonstrate that cats, as well as primates, can produce very short latency goal-directed saccades.

Acoustic Stimulation↗
PubMed1994

Orienting of attention and eye movements.

According to the premotor theory of attention, the mechanisms responsible for spatial attention and the mechanisms involved in programming ocular saccades are basically the same. The aim of the present experiments was to test this claim. In experiment 1 subjects were presented with a visual display consisting of a fixation point and four boxes arranged horizontally and located above the fixation cross. Two of the boxes were in the left visual hemifield, two in the right. A fifth box was located on the vertical meridian below the fixation cross. Digit cues indicated in which of the upper boxes the imperative stimulus was most likely to appear. Subjects were instructed to direct attention to the cued box and to perform a saccadic eye movement to the lower box on presentation of the imperative stimulus. The trajectory of the saccades deviated contralateral to the hemifield in which the imperative stimulus was presented. This deviation was larger when the hemifield where the imperative stimulus was presented was the cued one. In experiment 2, the visual display consisted of five boxes forming a cross. The central box served as a fixation point. The cue was a small line, linked to the central box, pointing to different directions and indicating where the visual imperative stimulus would appear. In 50% of trials, the imperative stimulus was a visual stimulus presented either in one of the lateral boxes or in the central one. In the remaining 50% of trials, the imperative stimulus was a non-lateralised sound. Half the subjects were instructed to make a saccade to the upper box at the presentation of the visual imperative stimulus and to the lower box at the presentation of the acoustic stimulus. Half the subjects received the opposite instructions. The results confirmed that the saccades deviate contralateral to the hemifield of stimulus presentation in the case of visual imperative stimuli. Most importantly, they showed that the saccades deviate contralateral to the cued hemifield, also in the case of acoustic imperative stimuli. Experiment 3 was similar to experiment 2. It confirmed the results of that experiment and showed that slow ocular drifts, which are observed in the time interval between cue and imperative stimulus presentation, cannot explain the ocular deviations. Taken together, the experiments demonstrate that spatial attention allocation leads to an activation of oculomotor circuits, in spite of eye immobility.

Attention↗
PubMed1978

The retinotopic distribution of visual callosal projections in the suprasylvian visual areas compared to the classical visual areas (17, 18, 19) in the cat.

The distribution of the interhemispheric projection from area 17 and 18 was studied using the anterograde degeneration technique. Besides the classical visual areas (17, 18, 19), area 21 and several visual areas in the middle suprasylvian sulcus also received visual callosal input. In the four terminal areas of the middle suprasylvian sulcus the projection was found to be focused on representations of the ventrical meridian including the area centralis, as in the classical visual areas. An increase of the width of visual field represented in the zone of callosal terminations can be seen from area 17 through area 18 to area 19 and possibly this trend continues in the suprasylvian visual areas.

Animals↗
PubMed1978

Functional organization in the cat's pulvinar complex.

The responses of 192 single units in the cat's pulvinar-complex, comprising the inferior, medial and lateral pulvinar nuclei, were studied in paralysed cats, lightly anaesthetized with N2O/O2 supplemented with pentobarbitone. About 60% of the cells were visually driven and their receptive fields classified as either diffuse, concentric, movement sensitive, direction sensitive or orientation sensitive. The response fields of such cells were commonly large. Response field maps for the movement and direction sensitive cells formed a heterogenous population with uniform on-off fields to more complex arrangements with on- or off-centres, often with only partial surrounds; other cells responded exclusively to moving stimuli. A dual representation of the visual field was found in the pulvinar-complex corresponding to the striate and tectal recipient zones described anatomically by others. The representation in the striate recipient zone comprised an oblique column running medio-laterally and rostro-caudally through the inferior pulvinar and lateral margin of the medial pulvinar. The peripheral visual field was represented laterally and the vertical meridian medially; the upper visual field was represented dorso-laterally in the medial pulvinar and the lower visual field caudo-ventrally within the inferior pulvinar. That this visuotopic organization corresponded to the striate recipient zone was established by tracing the retrograde transport of HRP. Medial to the striate zone evidence for a second visual field representation was found, apparently more randomly organized than the striate zone, corresponding to the presumed tectal recipient zone. These results support the assertion that cytoarchitectural boundaries do not necessarily delineate functional (visuotopically organized) regions. These observations suggest caution when comparing cytoarchitecturally defined regions between species; rather, 'functionally equivalent' regions should be compared.

Animals↗
PubMed1987

Electrophysiological evidence for interhemispheric connections in the anterior ectosylvian sulcus in the cat.

We report electrophysiological data regarding the contribution of the corpus callosum to visual responses in the cortex around the anterior ectosylvian sulcus (AES). The experiments were performed in cats in which the optic input from each eye was surgically restricted to the ipsilateral hemisphere (split-chiasm cats), and where neuronal responses to stimulation of the contralateral eye were mediated by interhemispheric connections. A very high proportion of cells were driven by stimuli presented to either eye indicating that they were activated not only through an intrahemispheric pathway from the ipsilateral eye, but also through an interhemispheric pathway from the contralateral eye. With few exceptions, both receptive fields (RFs) of each binocular neuron abutted or were in the vicinity of the vertical meridian. All neurons responded well to moving stimuli and most of them showed directional selectivity. A few cells were activated by stimuli moving in depth. Following an additional section of the posterior half of the corpus callosum, cells in AES responded only to stimulation of the ipsilateral eye, demonstrating thus that the input from the contralateral eye was conveyed by this part of the corpus callosum. By contrast following a section of the anterior half of the corpus callosum, all visually responsive AES neurons were binocularly activated. These results suggest that the interhemispheric visual input to this ectosylvian region is conveyed via a polysynaptic loop involving visual cortical areas that are connected through the posterior portion of the corpus callosum.

Animals↗
PubMed1979

Development of X- and Y-cells in kittens.

A contrast reversal stimulus was used to classify the retinal ganglion cells of kittens 3--12 weeks of age. At 3 and 4 weeks of age, the majority of the units were classified as Y-cells. The percentage of X-cells was similar to that of the adult at 5--6 weeks of age although other response properties were not adult-like. The angular size of the receptive field center was significantly larger than that of the adult through 5--6 weeks of age. An estimate of the position of the vertical meridian was obtained from the positions of the receptive fields in the visual field which permitted the calculation of the posterior nodal distance in kittens of various ages. From the posterior nodal distance, the linear extent of the receptive field center was determined. This showed that there is only a very slight increase in the linear size of the receptive field center from 3 weeks to adulthood.

Age Factors↗
PubMed1979

An estimation and application of the human cortical magnification factor.

Comparisons of the published data on the density D of receptive fields of retinal ganglion cells and on the cortical magnification factor M indicated that M2 is directly proportional to D in primates. Therefore, the human M can be estimated for the principal meridians of the visual field from the density-distribution of retinal ganglion cells and from the density of the centralmost cones. Using the previously published empirical data, we estimated the values of the human M and express the values in four simple equations that can be used for finding the value of M for any location of the visual field. The monocular values of M are not radially symmetric. These analytically expressed values of M make it possible to predict contrast sensitivity and resolution for any location of the visual field. We measured contrast sensitivity functions at 25 different locations and found that the functions could be made similar by scaling the retinal dimensions of test gratings by the inverse values of M. Visual acuity and resolution could be predicted accurately for all retinal locations by means of a single constant multiplier of the estimated M. The results indicate that the functional and structural properties of the visual system are very closely and similarly related across the whole retina. Visual acuity, e.g., bears the same optimal relation to the density of sampling executed by retinal ganglion cells at all locations of the visual fields.

Brain Mapping↗
PubMed1979

14C-deoxyglucose mapping of orientation subunits in the cats visual cortical areas.

The orientation domain in the cortical visual areas of anesthetized cats has been investigated by employing the 14C-deoxyglucose technique (Sokoloff et al., 1977). Orientation subunits (OS) are seen in the first (V1), the second (V2) and the third visual area (V3) as well as in the visual areas of the suprasylvian sulcus. In the latter regions OS are less elaborated than in V1, V2, and V3. The OS are continuous through all cortical layers; in V1 however, only weak label is detected in layer 4C. In V1, V2, and V3 the width of the OS is about 0.4 mm and the average distance between two OS centers is 0.9 mm. The spatial pattern of the OS seems to be more regular in the visual field periphery than in regions representing the vertical meridian.

Animals↗
PubMed1981

A quantitative analysis of the direction-specific response of Neurons in the cat's nucleus of the optic tract.

All cells in the nucleus of the optic tract (NOT) of the cat, that could be activated antidromically from the inferior olive, were shown to be direction-specific, as influenced by horizontal movements of an extensive visual stimulus. Cells in the left NOT were activated by leftward and inhibited by rightward movement, while those in the right NOT were activated by rightward and inhibited by leftward movement. Vertical movements did not modulate the spontaneous activity of the cells. The mean spontaneous discharge rate in 50 NOT cells was 30 spikes/s. This direction-specific response was maintained over a broad velocity range (Less Than 0.1 degrees - Greater Than 100 degrees/s). Velocities over 200 degrees/s could inhibit NOT cells regardless of stimulus direction. All cells in the NOT were driven by the contralateral eye, about half of them by the ipsilateral eye also. In addition, activation through the contralateral eye was stronger in most binocular units. Binocular cells preferred the same direction in the visual space through both eyes. An area approximately corresponding to the visual streak in the cat's retina projected most densely onto NOT cells. This included an extensive ipsilateral projection. No clear retinotopic order was seen. The most sensitive zone in the very large receptive fields (most diameters being Greater Than 20 degrees) was along the horizontal zero meridian of the visual field. The retinal input to NOT cells was mediated by W-fibers. The striking similarities between the input characteristics of NOT-cells and optokinetic nystagmus are discussed. The direction selectivity and ocular dominance of the NOT system as a whole can provide a possible explanation for the directional asymmetry in the cat's optokinetic nystagmus when only one eye is stimulated.

Animals↗
PubMed1977

Bilateral lesions of the medial longitudinal fasciculus in monkeys: effects on the horizontal and vertical components of voluntary and vestibular induced eye movements.

Bilateral transections across the brainstem interrupted the medial longitudinal fasciculus (MLF) in three monkeys trained to make eye movements while subjected to horizontal or vertical angular accelerations. Eye movements measured before and after the lesion revealed deficits in both voluntary and vestibular compensatory eye movements; the deficits differed in the horizontal and vertical directions. Vertical saccades in both directions were normal but eccentric positions of fixation could not be maintained; a drift toward the midline followed by a corrective saccade produced vertical fixation nystagmus. Furthermore, the vertical vestibulo-ocular reflex (VOR) was abolished and vertical smooth pursuit was impaired. Along the horizontal meridian, adduction across the midline could not be achieved during either saccades, smooth pursuit, or the VOR. Temporal saccades were normal whereas nasal saccades were considerably slowed. If the eye was not required to cross the midline, the phase shift during the VOR was within 15 deg of normal in each eye. The gain of the VOR was reduced to about 0.4 immediately after the lesion, but recovered within one month. These findings suggest that the MLF transmits quite different kinds of information to horizontal and vertical oculomotoneurons and that deficits in vertical eye movements may be a sensitive indicator of anterior internuclear ophthalmoplegia.

Animals↗
PubMed1980

Meridional amblyopia in monkeys.

Contrast sensitivity as a function of the orientation of a grating stimulus was determined by behavioral methods for four rhesus monkeys. Two of the monkeys had been reared with normal binocular experience, had spherical refractive errors, and showed a normal oblique effect. The other two monkeys which had been reared with one eyelid sutured (which was still sutured during these experiments), showed astigmatic refractive errors in the non-deprived eye and grating contrast sensitivity as a function of orientation that was correlated with the principal meridians of their astigmatism. Control experiments showed that the meridional amblyopia was not due to an uncorrected refractive error. Reaction time measures of contrast sensitivity for suprathreshold grating patterns showed that meridional amblyopia was not present for high contrast gratings.

Animals↗
PubMed1983

Retinotopic scatter of optic tract fibres in the cat.

The retinal fibers in the optic tract (OT) of the cat have a roughly retinotopic arrangement. The retinotopic scatter of OT fibres at the rostral pole of the superior colliculus (SC) and at the lateral margin of the lateral geniculate nucleus (LGN) was investigated using the retrograde transport of horseradish peroxidase. Small lesions and injections were made in the tract and from the distribution of labelled ganglion cells in the retina the retinotopic precision was measured. At an eccentricity of 30 degrees along the horizontal meridian the vertical scatter was 20-30 degrees. This is similar to the precision of the map in the SC. However a comparison with the retinotopic map of the LGN shows the precision there to be much better.

Animals↗
PubMed1984

Organization and properties of visually responsive neurones in the suprageniculate nucleus of the cat.

Visually responsive neurones of the cat's suprageniculate nucleus were categorized according to their responses to a variety of different types of light stimuli. Their velocity preferences were assessed quantitatively and have been found to predominate in the high range. The positions and dimensions of their receptive fields were determined and these tended to be found within a zone between the vertical meridian and 30-35 degrees. Receptive fields had mean diameters smaller than those reported by others for the pulvinar-LP complex. From these and other electrophysiological data, inferences have been made of the likely sources of afferents providing visual driving. A proposal is offered for SGn visuotopic organization based on correlations of receptive field location with cell position, as determined through electrode track reconstructions.

Animals↗
PubMed1981

Visually triggered eye-arm movements in man.

The degree of temporal coupling and the nature of temporal ordering between the gaze (eye-head) and arm motor systems was studied in normal subjects by measuring the reaction time, RT, of each system to randomly generated visual signals presented along the horizontal meridian: (1) at two spatial locations, 15.5 degrees and 29.1 degrees, (2) to the right and left of a central fixation point, and (3) with and without room illumination. Upon detecting the visual signal, the subject was instructed to guide the arm from its rest position upon a supporting table and to extinguish the light source by touching a metal disc enclosing the stimulus "as quickly and accurately as possible." The results indicated (1) saccadic eye motion initiated gaze towards the target, (2) a change in the eccentric position of the target was associated with alteration of the eye and arm RT by a similar value; the interval between eye and the subsequent arm RT was invariant with spatial location no matter the presence or absence of room illumination, and (3) the arm RT increased when visual information of the environment was not available. It is postulated that a visual stimulus triggers a command system releasing a patterned sequence of eye-hand-arm motion; the initiation of motion in these motor systems is based upon the same retinal error calculation; however, no rigid rule can be established for the serial ordering or temporal sequencing of motion between the triggered motor systems. The temporal arrangement between head and arm with eye can be modified, at least in part, by alterations in supraspinal control of postural mechanisms and/or motoneuronal excitability of the responding muscles prior to motion.

Adolescent↗
PubMed1980

Functional changes across the 17-18 border in the cat.

Changes in velocity sensitivity, receptive field (RF) position, and RF size were investigated in long oblique penetrations crossing the 17-18 border. The penetrations were histologically reconstructed and the border determined by cytoarchitectonics. In cortex subserving central and paracentral vision change in velocity sensitivity allowed a reasonable physiological identification of the 17-18 border. The physiological border correlates well with the histological border zone, best with its medial edge. Changes in RF position and RF size are of little use for physiological identification of the border in this region. In this cortical region area 18 representation of the vertical meridian (VM) has a high magnification factor. In cortex subserving peripheral vision, the change in velocity sensitivity was small and the change in RF position coincided with the cytoarchitectonics.

Animals↗
PubMed1984

Cell populations of the ganglion cell layer: displaced amacrine and matching amacrine cells in the pigeon retina.

The proportion and size distribution of ganglion and non-ganglion cells in the ganglion cell layer of different areas of the pigeon retina was examined in whole-mounts of the retina by retrograde axonal transport of horseradish peroxidase (HRP) from large brain injections. A maximum of 98% of cells were labelled in the red field and a maximum of 77% in the peripheral yellow field. Unlabelled cell bodies were 30% smaller than labelled ganglion cells and had a mean diameter of 6.2 microns and a size range of 4 to 9 microns. The morphology of cells in the ganglion cell layer was examined by Golgi staining of retinal whole-mounts. Small glia, displaced amacrine and ganglion cells were found. Displaced amacrine cell bodies were about 30% smaller than ganglion cells and their size distribution was similar to the unlabelled cells in HRP preparations. Displaced amacrine cells had small rounded cell bodies (mean diameter 6.2 microns) increasing in size with eccentricity, and a unistratified dendritic tree of fine, nearly radial, varicose dendrites in sublamina 4 of the inner plexiform layer. They had elliptical dendritic fields (mean diameter 66 micron) aligned parallel to the retina's horizontal meridian. A population of amacrine cells was found with somas at the inner margin of the inner nuclear layer and soma and dendritic morphology matching those of displaced amacrines. These amacrine cells had unistratified dendritic trees at the junction of sublaminae 1 and 2 of the inner plexiform layer. Pigeon displaced amacrine cells and their matching amacrines are similar to starburst cells of the rabbit retina.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Differences of visual field representation in the medial and lateral banks of the suprasylvian cortex (PMLS/PLLS) of the cat.

We have studied the orderliness of representation of visual space in the medial and lateral banks of the middle suprasylvian sulcus. Penetrations were made either parallel to the sulcus, in one bank or the other, or vertical, thus crossing the sulcus between the postero-medial (PMLS) and posterolateral (PLLS) divisions of this area. In some cases we found clear evidence for topographical order in the representation of the visual field with a tendency (greater in PMLS than in PLLS) for the receptive fields of cells recorded deeper in the walls of the sulcus to lie closer to the area centralis, but along many penetrations the receptive fields were so large and so scattered that no retinotopic arrangement could be discerned. In PMLS the receptive fields of the majority of units we studied were centered below and close to the horizontal meridian, whereas in PLLS they were distributed over both the upper and lower visual fields with an over-representation of the upper field. Receptive fields were significantly larger in PLLS (mean field area = 442.2 deg2) than in PMLS (mean area = 154.4 deg2); there was also less clear correlation between receptive field size and eccentricity in PLLS (correlation coefficient = +0.25) than in PMLS (corr. coeff. = +0.72). Analysis of the distance between the receptive field centres of consecutively recorded units demonstrated that the mean scatter in both PMLS and PLLS amounts to about half the average receptive field diameter. In summary the topographical representation of visual space is less orderly in PLLS, and may involve a wider area of the visual field. These findings may relate to the segregated visual cortical and extrageniculate thalamic connections that the medial and lateral banks of the LS receive.

Animals↗